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The Carbohydrates of Food and Their Absorption - Physiology and General Pathology of Sugar Excretion

blood, carbohydrate, starch and absorbed


In order to gain a clear idea of the ultimate fate of the carbohy drates in the body we shall do well to begin with those of the food.

Starch.—The most important alimentary carbohydrate is starch (amylum). This is a material which is compounded of several small er carbohydrate molecules, and which is for this reason called poly saccharid. Starch cannot be absorbed as such, and must first be decomposed by a process of fermentation into the easily soluble carbo hydrates. This decomposition is a process of division in which several smaller carbohydrate molecules (monosaccharids and cisac charids) are formed from the large carbohydrate molecule (polYSac charid). The polysaccharid glycogen has to undergo a similar con version before it can be absorbed.

The ferment (diastase) through the action of which this division is accomplished is found more especially in the buccal secretions and in the pancreatic juice, but it seems to be entirely wanting nowhere in the body.

Diastase gives rise to the formation from starch of the following bodies, some of which are produced consecutively, others simultane ously, viz., soluble starch (amidulin), erythrodextrin, achrooclextrin, isomaltose, and maltose. As these division-products of starch pass into the intestinal wall and portal vein they undergo a further change, being almost entirely converted into grape sugar (glycose, glucose, or dextrose). Dextrin and maltose meet, of course, the same fate when

taken as such in food or drink.

Cane sugar (saccharose) is a disaccharid; it is split up in the ali mentary canal, through the action of acids, ferments, and bacteria, into its two components, grape sugar and fruit sugar (levulose), and in this shape is absorbed. It is only when cane sugar has been in gested in very large quantity that any of it passes unconverted into the blood.

Fruit sugar (levulose, present in ripe fruits and in honey) is taken into the blood unchanged.

Milk sugar (lactose) also passes unchanged into the blood.

Cellulose is probably never absorbed, although a portion of it is lost in the intestinal canal, it being very easily fermented and changed by the action of the bacteria into methan, carbonic acid, acetic acid, and butyric acid.

From the intestinal wall the carbohydrate stream flows through the portal vein to the liver. According to the nature of the food in gested various forms of carbohydrates take part in this procession— glucose, levulose, lactose, saccharose, and traces of dextrin and mal tose. It is furthermore evident that the richness of the portal blood in carbohydrates must be very variable. While in fasting or flesh and-fat-fed clogs the percentage of carbohydrates in the blood of the portal vein is from 0.10 to 0.15, von Mering found it increased to 0.4 and more after feeding the animals with carbohydrates.